A computer-based file storage and retrieval system will be developed to allow real-time entry and retrieval of cardiovascular data. The file system to be designed will be hybrid in nature, in that it will contain a variable-position, variable-length file for entry of information and a fixed-position file for retrieval. The retrieval system will allow real-time conversational questioning of the acquired data base. Specific entries in a patient's record can be retrieved. Statistical tests can also be performed within specified subgroups. An additional component of this research will involve development of clustering techniques in order to identify groups of patients whose data is similar. These clusters will be used to: a) generate keys for efficient filing of data; b) identify clinically-useful subsets of disease; and c) identify homogeneous groups suitable for randomization in experimental trials associated with chronic disease.